Electrostatic Atomisation & Spraying
The efficient atomisation of liquids into a uniformly dispersed aerosol and the application of surface coatings of controlled thickness can be achieved using electrostatic techniques. Many paints, resins, solvents and oils can be atomised into near equal-sized droplets and sprayed electrostatically without the use of atomising air or significant hydraulic pressure.
Airless application of liquids
Electrostatic atomisation is achieved by directing the liquid to be sprayed through an electrified applicator - this may be a nozzle, array of tubes, blade or other geometry suited to the spraying requirements and conditions. As the charged liquid leaves the applicator it is dispersed by the electric field (which is established between the emerging liquid and the work-piece or a counter electrode). Depending on the operating conditions and physical properties of the liquid, a liquid jet extends toward the work-piece with the end of the jet disrupting into a stream of uniform droplets.
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The advantages of airless electrostatic spraying over conventional air atomisation are considerable and include uniformity of deposition, minimal wastage of liquid and greater control. In addition, electrostatic applicators are far less prone to blockage than conventional nozzles. There are significant environmental and health and safety benefits too. Since the droplet cloud is charged and attracted to the target, there is virtually no overspray. The spraying operation produces no significant air currents and, with a properly balanced system, no particulates are left in the atmosphere.
Although this technique works well with many liquids, water-based liquids have a relatively high electrical conductivity and can not be easily atomised by electrostatic forces alone. In these cases a ‘hybrid’ applicator which incorporates mechanical atomisation together with electrostatic charging can be utilised. Such systems are used in crop-spraying and combine high liquid throughputs with very high charging levels to improve deposition and transfer efficiency.
Printing and Coating
Electrostatics has been closely linked to printing and coating technology for many years. In partnership with a major international company Wolfson Electrostatics developed a novel system for applying a thin coating of resin to lithographic plates. This patented technology is installed on production lines throughout the world and is required to operate continuously and virtually maintenance free. The technology is still supplied direct by Wolfson Electrostatics to the printing and photographic industry.
Wolfson Electrostatics is currently looking at developing new techniques in the industry for the application of specialist coatings to a variety of substrates, including plastic films, fabrics and glass. Projects have included improving ESA (electrostatic assist) in gravure and other printing techniques, and the efficient application of thin uniform coatings to ‘difficult’ surfaces such as high-speed plastic webs.
For further information on Printing & Coating contact Wolfson Electrostatics.